The monomer, 2,2,4,4-tetramethylcyclobutane-1,3-diol, (TMCD) is an important intermediate for producing a variety of polymeric materials which possess advantageous properties. For example, polyesters derived from dicarboxylic acids and 2,2,4,4-tetramethylcyclobutane-1,3-diol can possess higher glass transition temperatures, impact strength, weatherability, and hydrolytic stability in comparison to many other polyesters prepared from other commonly-used diols. TMCD (II) can be prepared by the catalytic hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione (I), as illustrated in following schematic:
Hydrogenation of 2,2,4,4-Tetramethylcyclobutane-1,3-dione

The hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione produces 2,2,4,4-tetramethylcyclobutane-1,3-diol as a mixture of cis and trans isomers. For example, U.S. Pat. No. 3,190,928 discloses the hydrogenation of 2,2,4,4-tetramethylcyclobutane-1,3-dione using nickel- or ruthenium-based catalysts to produce 2,2,4,4-tetramethylcyclobutane-1,3-diol with molar cis:trans ratios that can vary widely from about 0.5 to about 1.2. The cis:trans ratio is typically about 1:1 to 1.5:1 in most solvents. The cis:trans ratio is even lower when a nickel catalyst is used for the hydrogenation. The only methods believed to be known in the art to obtain primarily cis-2,2,4,4-tetramethylcyclobutane-1,3-diol involve physical separation of the cis isomer from trans isomer. In order to obtain high overall conversion to cis-2,2,4,4-tetramethylcyclobutane-1,3-diol in these physical separation processes, the recovered trans-2,2,4,4-tetramethylcyclobutane-1,3-diol must be isomerized again to a mixture of cis and trans isomers, thus requiring even more processing and a large recycle loop.
Also, catalysts that produce the most desirable ratio of cis:trans isomers may not give the best yields or highest rates of hydrogenation. The cis:trans isomer ratio of 2,2,4,4-tetramethylcyclobutane-1,3-diols can influence important properties such as, for example, the glass transition temperature, impact strength, and crystallization rate of the polyester polymers prepared from them. A cis:trans ratio that varies widely, in turn, can give polyesters with inconsistent and/or undesirable properties. A process that produces high cis:trans ratios, therefore, would be desirable in order to produce 2,2,4,4-tetramethylcyclobutane-1,3-diol with consistently high cis:trans ratios regardless of the hydrogenation catalyst used. Such a process also would enable the efficient production of polyesters from 2,2,4,4-tetramethlycyclobutane-1,3-diol with properties that can be tailored to a variety of applications.